{
  "bibcode": "2005GCN..3554....1K",
  "body": "H11603:  An X-ray flare from V4641 Sgr, or a possible XRF\n\nJ. Kotoku, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley, \non behalf of the HETE Science Team; \n\nM. Arimoto, T. Donaghy, E. Fenimore, M. Galassi, C. Graziani, \nM. Maetou, M. Matsuoka, Y. Nakagawa, T. Sakamoto, R. Sato, \nY. Shirasaki, M. Suzuki, T. Tamagawa, K. Tanaka, Y. Yamamoto, \nand A. Yoshida, on behalf of the HETE WXM Team; \n\nN. Butler, G. Crew, J. Doty, G. Prigozhin, R. Vanderspek, \nJ. Villasenor, J. G. Jernigan, A. Levine, G. Azzibrouck, J. Braga, \nR. Manchanda, and G. Pizzichini, on behalf of the HETE Operations and \nHETE Optical-SXC Teams; \n\nM. Boer, J-F Olive, J-P Dezalay, and K. Hurley, on behalf of the HETE \nFREGATE Team; \n\nreport:\n\nThe HETE WXM instruments detected an untriggered burst H11603 at\n04:05 UT on 26 June 2005.  The burst is extremely soft (most photons <\n5 keV), has a spiky profile with timescale of 1 second, and the\nduration is about 100 sec.  The peak flux (2-30 keV over 5 s)\nwas ~7x10^-8 erg cm^-2 s^-1.\n\nH11603 is localized by the WXM to a circle of radius of 6' centered \nat RA = 18h 19m 38s, Dec = -25d 26' 30\" (J2000).  A GCN Ground\nAnalysis Notice was issued.\n \nIts position is marginally consistent with that of \nV4641 Sgr = SAX J1819.3-2525 = XTE J1819-254.\nExamination of earlier data revealed another event at 03:01 UT on 26\nJune 2005, consistent with these locations.  This source was recently\nreported to be X-ray active by Swank, Smith and Markwardt (ATEL #536).\n\nThe spiky profile of the burst is similar to that observed for the\nX-ray flares from V4641 Sgr (e.g. Wijiand and van der Klis 2000, ApJ\n528, L93).  With a preliminary analysis we find the burst has a\nspectrum consistent with a blackbody with kT=1 keV with a hard tail,\nwhich is also similar to the X-ray spectrum reported for V4641 Sgr by\nearlier observations (e.g. in't Zand et al. 2000, A&A 357, 526).\n\nThus H11603 is very likely to be a X-ray flare from V4641 Sgr, \nand not an XRF of an extragalactic origin, although we cannot\nabsolutely exclude the possiblity.\n\nOptical and X-ray follow-up observations of the counterpart are\nencouraged. \n\nThis message may be cited.",
  "circularId": 3554,
  "createdOn": 1119819969000,
  "email": "gbc@space.mit.edu",
  "subject": "H11603:  An X-ray flare from V4641 Sgr, or a possible XRF",
  "submitter": "Geoffrey B. Crew at MIT/HETE  <gbc@space.mit.edu>"
}